1. Field of the Invention
This invention relates generally to battery/fuel cell technologies, and more specifically to rechargeable battery. In particular, this invention relates to the construction of battery electrodes and an energy storage medium that allows recharging the battery by replacement of the energy storage medium rather than by conventional recharging techniques, such as by reverse chemical reactions driven by the application of electrical energy or replacement of battery electrodes. The rechargeable batteries of the present invention are particularly suited for use with electro-motive vehicles and bulk energy storage systems.
2. Description of the Related Art
With the increasing awareness of environmental damage caused by the combustion of fossil fuels, the search for a replacement for such fuels has intensified. Due to the large volume of greenhouse and other undesirable gases produced by the internal combustion engines used to power motor vehicles, it has become especially critical to find a suitable non-polluting replacement power source for these transportation vehicles. One promising replacement for the fossil fuel powered vehicle so prevalent today is the electro-motive vehicle. However, before the electro-motive vehicle will become a practical replacement for these vehicles, one major obstacle must be overcome. This major obstacle is the development of a means for storing and converting electrical energy which will allow an electro-motive vehicle to deliver the acceleration and range performance similar to that obtained now by internal combustion engines. To date, this obstacle has not been surmounted.
Electro-motive vehicles commonly use batteries to store and convert chemically stored energy to electrical energy required for operation. In these and other applications where large amounts of electrical power and energy are required, the present state of the art requires that the volume and weight of batteries be very large and that the batteries be subjected to a lengthy recharge period on a regular basis. In many cases, these characteristics are not desirable, and have hindered the widespread development of the electro-motive vehicle applications.
For example, in applications such as those involving electric vehicles, the total amount of electrical power required is large to provide the desired acceleration and the energy requirements are large to provide the desired range. The resulting volume and weight of the batteries is excessive and must be minimized to make electric vehicles practical as well as cost effective. In addition, the recharge time must be minimized to make electric vehicle use practical. Conventional batteries are poor candidates for electric vehicles because they also require a long time period to recharge that is unacceptable to customers that are familiar with internal combustion engine powered vehicles. This characteristic is primarily due to the fact that all available electrode material must be replenished through electrochemical reactions during the recharge cycle to increase the energy storage density and thus the time between recharging.
Batteries typically store energy chemically in compounds deposited on the battery electrodes or plates. Electrical current is generated through chemical reactions at the plate or electrode surfaces, which convert the plate compound to another compound and produce an ion or electron. Ions are then transported through the electrolyte between the plates to complete the electrical circuit. Therefore, when the compounds deposited on the electrodes have all been chemically converted, the battery is discharged and the available energy is zero.
In a typical electrochemical battery system, the chemical reactions occurring at the electrode plates are classified as oxidation and reduction. The electrode plate where oxidation occurs is called the anode because electrons are produced in the electrode plate material during the oxidation reaction. Conversely, the electrode plate where reduction occurs is called the cathode because electrons are used during the reduction reaction. The combination of a given anode material with a given cathode material is known as an electrochemical couple. The selection of the electrochemical materials that make up an electrochemical couple is made by comparing the tendency of each material to undergo a reduction reaction when coupled to a standard hydrogen electrode, known as the "standard reduction potential". The material with the higher standard reduction potential is selected for the cathode and the material with the lower reduction potential is selected for the anode. The difference in the standard reduction potential between the two materials determines the voltage generated by the electrochemical couple.
For conventional batteries, the amount of energy storage in a battery depends upon the amount of chemical compounds that are in contact with the battery electrodes. The rate at which battery energy can be supplied or the power can be made available is dependent upon a number of parameters, including the electrode surface area available for chemical reactions to take place. Conventional batteries use porous electrode plates to increase the area of the electrode surface available for chemical reactions. High power density batteries or batteries that can provide a large energy in a short period of time require chemical access to a large volume or surface area of active chemical compounds on the battery plates. For example, in a common lead acid battery in the charged state, one of the active chemical plates consists of lead, which is present in a "spongy" form to increase the active surface area. The surface of the lead plate or electrode is converted to lead sulphate during discharge to a depth determined by the penetration of the chemical reaction into the surface. Thus, in a conventional lead acid battery, only a small fraction of the lead plate or electrode surface is exposed to the electrolyte in the electrical energy conversion process such that chemical reactions must diffuse through previously converted material.
Batteries for electric vehicles are designed primarily around two specifications, the required power necessary for acceleration and the required energy required for range of travel. For example, a 200 hp equivalent electric motor requires a peak electrical power source of approximately 150 kW. Secondly, the continuous power required to cruise an electric vehicle at 70 mph is approximately 25 kW. A three hour cruise would require a battery to deliver a total energy of 75 kW-hr and result in a range of 210 miles. A reasonable battery weight for a full sized vehicle is approximately 330 lbs or 150 kG which results in a desired power density of 1000 W/kG and an energy density of 500 W-hr/kG. Conventional batteries can deliver only about 1/10 th of the power density and the energy density desired above resulting in a battery weight of 3300 lbs. Thus existing batteries result in a system weight which is approximately 10 times that desired.
One way of reducing battery weight and increasing the run time between recharge cycles is to increase the energy density of the battery. The energy stored in a battery is dependent upon the chemical characteristics of the electrochemical couples selected for use in the battery. Because the battery volume must contain all of the electrochemical energy in the form of active material in contact with the battery electrodes or plates, a lot of effort has been expended in the past toward developing high-energy electrochemical couples to increase the battery electrochemical energy density.
Another way of reducing battery weight and increasing effective run time is by altering the physical design of the battery electrode plates. Recharging a battery restores the active compounds on the battery plates through reverse chemical reactions driven by the application of electrical energy. Recharging a battery takes a long period of time due to the nature of the chemical reaction and the desire to restore the active compounds through chemical reactions as far as possible into the surface of the battery plates. Restoring the active materials through chemical reactions is very slow since the reactions take place at the surface of the material and migration of the reformed material into the interior of the electrode is extremely time consuming, if possible at all.
The size and weight of the battery could be reduced if a small layer of active material could be continually replaced on the electrode surface as other active material is converted during discharge. In the past, several mechanical schemes have been innovated to physically move or replace the plates in a battery so as to improve the access of the electrolyte chemical to the plate or electrode material and to increase the amount of energy produced by the battery. The goal of this prior research has been to create a battery in which the active chemical material could be replaced periodically with a liquid material in a manner similar to refueling a conventional combustion engine using liquid fuel or in which the active chemical material could be replaced continually during operation as in a fuel cell. In this manner, the energy storage function of the battery could be separated from the energy conversion function and each optimized to provide an improved energy storage and conversion system.
Still other ways of improving the efficiency and output of battery cells have been attempted. For example, U.S. Pat. No. 3,409,471 to Sturm et al. discloses a method for operating a catalytic battery system utilizing magnetic fields and ferromagnetic catalyst materials.
In this system, loose ferromagnetic catalyst materials are mixed with electrolyte and charged with an electro-active gas or organic compound by adsorption. Catalysis is a three body situation where the presence of the catalyst increases the probability of reaction between the other two bodies. By definition, a catalyst is not used up in a reaction, but is used to encourage a reaction. Acceptable compounds for absorption on the ferromagnetic carrier of the catalyst, described in this patent are H.sub.2, O.sub.2, methanol and ethanol. In the operation of the catalytic battery system, the electrolyte and gas/liquid charged ferromagnetic catalyst material is placed in a cell, and the catalyst material is attracted to an electrode by a magnetic field, where the electro-active compounds undergo electron exchange and are released from the region in which the catalyst, the electrode and the fuel coincide such as the surface of the catalyst material. Although the system offers increased access to the electro-active material contained within the battery, it fails to offer the high energy density required for applications such as powering electric vehicles, because the density of the electro-active material, either gas or liquid, is insufficient to provide the current density necessary. Because the battery system relies on catalytic adsorption of electro-active compounds onto the catalyst material, these compounds are likely limited to gases and liquids.
Therefore, the range of electrochemical couples that may be used in the Sturm patent appears to be very narrow and those couples available lack the high energy density required for a practical power source for an application such as an electro-motive. As an additional disadvantage, the adsorption/desorption cycle of the catalytic battery requires that the catalyst material can only be regenerated by physical contact with the electro-active material itself rather than by more conventional recharging means, such as application of reverse current. This means that it may be necessary to handle large amounts of potentially hazardous materials, such as H.sub.2 in the recharging procedure. Finally, in some cases, the limited stability of the adsorption process may render long term storage of the charged catalyst material impractical, for example, if the material must be stored under pressure in the case of gas absorption.
Despite past efforts, existing and presently planned battery systems do not provide sufficient energy storage density in a reasonably sized package so as to allow long trips in electric vehicles. In addition, existing and planned battery systems require long periods of time to recharge the energy storage medium and are limited in the number of times they may be recharged due to deterioration of battery components. Therefore, at this time electric vehicles utilizing electric energy storage systems are not economically or operationally feasible, nor do they compare in viability with other forms of transportation.
Accordingly, it is an object of the present invention to provide a battery system that is rechargeable by replacing a specially designed liquid fuel slurry in the battery, thus making the recharging process similar to refueling a gasoline powered automobile.
It is also an object of the invention to provide a battery system in which the fuel slurry is continuously replaced or recharged by circulation through the battery, as in a liquid fuel cell.
A further object of the invention is to provide a battery system in which the effective area of the battery electrode-plate surface area is increased so as to increase the stored energy density and the rate at which electric energy can be removed.
Still another object of the invention is to provide a battery system structure that can utilize different types of liquid slurry fuel so that the same battery/fuel cell structure can be used with future battery fuel slurries that have been improved or changed.
Still another object of the invention is to provide a special type of battery slurry fuel that enables the multi-fuel, rechargeable battery and liquid fuel cell concept of this invention.
Still another object of the invention is to provide a method of contacting a liquid battery fuel slurry with the battery electrode plates that is compatible with continuous or bulk liquid recharging.
Still another object of the invention is to provide a method of using solid fuel coatings on ferromagnetic carriers to provide simultaneously, the large surface area and the active material density necessary at the electrode surface to produce the large current density required for electric vehicles and bulk energy storage systems.
Other and further objects, features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the following description of the preferred embodiments including the examples provided therewith.